CA1092014A - Method and apparatus for conservation of energy in a thermal oxidation system for use with a printing press - Google Patents

Abstract

Abstract of the Disclosure Solvents evaporated from ink solutions in the drying sections of a multi-station printing press can be converted into harmless carbon dioxide and water vapor by heating the dryer exhaust for a given time period above a given oxidation temperature. The amount of energy required to maintain the oxidation temperature is substantially reduced by preheating the solvent laden exhaust through the use of a pebble bed heat generator prior to introduction of same into the oxidation chamber. If gases containing a sufficient solvent concentration level are preheated above the solvent ignition temperature, the solvent itself will provide heat of combustion sufficient to maintain the oxidation process. With this degree of preheat, at high solvent concentration levels, not only is no additional fuel required, but excess heat is generated.
In order to maintain the system at minimum fuel consumption and eliminate the excess heat generated which is detrimental to operation of the oxidation chamber, a portion of the preheat section is bypassed by a selected amount of the exhaust such that the temperature in the oxidation chamber may be regulated.
Alternatively, the solvent concentration level of the exhaust can be lowered by mixing the dryer exhaust with the floor sweep exhaust (of substantially lower solvent concentration) in regulated proportions. The latter method has the advantage of providing floor sweep capability without increased cost.
Further, the use of solvent concentration (LEL) controls in the dryer sections can enhance the accuracy of the concentration control at the oxidation chamber and substantially reduce the size of the chamber by reducing the volume of exhaust to be processed.

Description

The present invention relates to~a thermal oxidation system for use ,~ with a multi-color rotogravure packaging/printing press or the like, and more "r' particularly, to a method and apparatus for energy conservation in such a ~:, thermal oxidation system.
The oxidation system of the present invention is designed primarily for use with rotogravure packaging/printing presses or the like and is there-for described in conjunction with such a press, for purposes of illustration.
However, it should be understood that the concepts herein described can be applied to any process where volatile fuel organic solvents are used and `;
normally emitted to the environment. Thus, the present invention should not . be construed as limited for use only on printing presses of the type described.
Rotogravure packaging/printing presses are currently widely used by ` packaging/printersO Air pollution standards require that the solvents present -in the exhaust gas from such a press be removed prior to introduction of .., ;~, the exhaust to the environmentO Moreover, it is necessary, to ensure the health of the individuals present in the pressroom during operation of the press, to continuously remove the solvent laden air from the floor of the pressroom. Unfortunately, a large amount of energy is required to perform these tasks with existing technology.
Two approaches are available for removing organic solvents from the exhaust of a rotogravure printing unit. The first method, commonly known as ;
~c solvent recovery, passes the solvent laden exhaust through an activated carbon ` bed, which, by means of an ion exchange process, retains the organic materials.
; ~ Usually two beds are provided, with one "on stream" and the other in a re-i cycled mode. Steam is used to purge the organic materials from the recycling bed and produce a water solvent mixture. The mixture is then separated in a decanter, and, if possible, the solvent reusedO
he second method for removing solvents is to utilize the organic solvents as a means of fuel by bringing the exhaust gas to a temperature about 3n 1~00F. If the exhaust gas is held at this temperature for about .6 seconds .,~.
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over 99% of the solvents are converted into harmless water vapor and carbon dioxide.
~ The solvent recovery method is economically feasible only for ink " preparations which are soluble in aliphatic hydrocarbon solvents and insoluble ... .
in water and which have a specific gravity of less than one. These Xinds of solvents can be recovered in their pure form through simple decanting and can be reused.
However, for the packaging industry, the inks utilized are often soluble in various organic solvents, as well as in water. Since each day totally different products are produced using various combinations of a variety ~:
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of differen~ solvents if solvent recovery was used, distillation of the end product would be required. Depending upon the product being processed and combination of the solvents used, various azeotropes (a combination of two .
different liquids which exhibits a lower or a higher boiling temperature than either of the pure components) would be produced. Because of the nature of these chemicals, it is impossible to distill the various solvents in pure form.
This, therefore, precludes the reuse of the end product. Thus, solvent re-covery cannot be used with these types of inks and the solvents must be oxi~
dized to purify the exhaust.
A variety of different thermal oxidation systems have been utilized.
One type of system utilizes a common afterburner. Unfortunately, such an ,. .
afterburner sys~em is not practical because it has excessively high energy requirements. A heat exchanger can be used to recover some of the energy of the exhaust from the afterburner. However, while this system is an improve-ment over the common afterburner, from an energy point of view, it is dis-ad~rantageous because of high maintenance costs and the inability to make same efficient with widely varying solvent concentrations. A catalytic afterburner has also been developed. The addition of the appropriate catalyst provides the ability to oxidize the organic materials at considerably lower tempera-,. ~.
~ 30 tures. However, while energy requirements are reduced in this system, the .~
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)14 ; catalytic beds are expensive and also require high maintenance.
Another concept that has been employed for pollution control is the use of thermal oxidation combined with energy recovery. This system involves heating the exhaust in a chamber to the required 1400F level for a given time period with recovery from the exhaust of sufficient BTU's to heat oil~ which is then used to preheat the process air in the dryer. Usually, the energy re-quired for process air heating is small in comparison to the energy subsequent-ly used to heat the process air to the 1400F level. Combining the two re-quirements has led to numerous difficulties with little success.
It has been recognized that it would be ideal to recover the heat generated in the exhaust of the thermal oxidizing unit, since this is the area where all thermal oxidizing units are deficient in energy conservation. The most efficient method of recovering the heat generated is an old concept em-ployed in steel and glass furnaces, commonly referred to as the pebble bed heat generator. One application of such a system tb ~l~minatesolvents in ex}laust gases is described by James Mueller in his United States Patent No.
3,895,918 issued July 22, 1975.
The pebble bed heat generator is utilized as a preheater. Air is ' taken from the dryers by blowers and driven through one pebble bed, which has previously been used as the exhaust to the chimney. The input air is pre-heatedl passed through the oxidation chamber, and then returned through a second pebble bed, which recovers the heat from this exhaust, reducing the ~, final temperature of the exhaust. An input-output damper is periodically switched to interchange the preheater from the exhaust, while simultaneously preheating the air with the energy stored in the pebble bed. More than two pebble beds may be used in the same system, if required. Natural gas or other fuel is utilized in the oxidation chamber in order to raise the level of the preheated gases to the oxidation temperature, approximately 1~00F.
:;., In addition to the high thermal efficiency of such a systeml the system has several other desirable characteristics. The pebbles in the pebble , ` - 3 -l.~9~
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bed are actually ceramic materials which can withstand very high temperatures.
As the solvent laden air flows through the preheated bed, it will release its heat of combustion with the energy absorbed by the ceramic materials, with no detrimental effect to the preheater and the heat of combustion can be utilized to reduce the amount of heat applied in the oxidation chamber. All of the axhaust gas is preheated to the 1400F level and thoroughly premixed by the structure of the elements in the bed so that the dwell tima (approximately .6 seconds, for 99% oxidation) can actually start from the time the exhaust gas ; leaves the preheat b0d, permitting the entire structure to be substantially smaller.
The high efficiency of the system provides the ability to use a very small burner, reducing energy consumption drastically over any other system currently available. Condensation cannot occur since the temperature of the exhausting air is always higher than the entrance temperature air. The system can be made extremely efficient when heating exhaust gas with little solvent ` content, permitting same to be used in conjunction with a pressroom floor ventilating system thereby cleansing the air in the pressroom. A flame using any energy source such as gas or oil can be employed within the oxidation " chamber. 5ince the entire oxidation chamber is maintained at the 1400F level, it is not necessary for the air to pass directly through the flame, as is com-mon with existing thermal oxidizing units that require the use of gas. More-., .
;~ over, all the products of combustion are oxidized, well below the temperatures at which point the oxides of nitrogen are formed. Also, since all of the air passing the flame is preheated to the 1400F temperature, there is no quench~ `-ing of the flame which produces oxides of nitrogen common in large power ~ boilers.

i In such a system, the heat of combustion released from the solvent .,,. ~
laden air can be used as a source of heat in the oxidation chamber as long as the gases are preheated above the solvent ignition temperature. The amount of heat of combustion which is generated will depend upon the amount of heat '.:

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- 1092~3L4 ' applied during preheating and the concentration of the solvent in the exhaust.
Below a given solvent concentration level (approximately 7.4% LEL ~Low Explo-sive Limit) concentration) additional heat must be introduced into the oxida-tion chamber to maintain the 1400F level required for the oxidation process.
However, above approximately 9.1% LEL, more heat than is required to maintain the oxidation process is generated. Because deterioration of the structure may result from the excess heat, it is necessary to regulate the amount of excess heat which is generated within the system.
One of the major drawbacks of conventional thermal oxidation systems, such as the one disclosed by Mueller, is the inability of these systems to ;~ function at high solvent level concentrations without deterioration. Such deterioration is costly in that it requires high maintenance costs and limits the useful life of the oxidation chamber.
It would be advantageous to have a method and apparatus for energy conservation in a thermal oxidation system wherein the heat of combustion of the organic solvents can be regulated to reduce fuel consumption and eliminate structure deterioration. In particular, it would be advantageous to have a method and apparatus for energy conservation in a thermal oxidation system wherein the degree to which incoming exhaust gase is preheated may be regulated ,.,:
and/or wherein the solvent level concentration in the exhaust gas may be regu-lated both in order to control the generated heat of combustion of the solvent and thus reduce fuel consumption. ~ !
It would also be advantageous to have a method and apparatus for energy conservation in a thermal oxidation system wherein the thermal oxida-,,.~;
-` tion system is efficient over a wide range of solvent concentrations and where-~ in same can be utilized in conjunction with a floor sweep ventilating system , in order to efficiently clean pressroom air: the floor sweep ventilation sys-tem becoming increasingly more efficient as the solvent concentration level increases.

It would further be advantageous to have a method and apparatus for - 5 _ ~' .

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energy conservation in a thermal oxidation system wherein deterioration of the structure of the thermal oxidation chamber and damage to the energy recovery system are virtually eliminated at high solvent concentration levels and where-in maintenance costs for the system are substantially reduced.
Accordingly, the present invention provides a thermal oxidation sys-tem adapted to remove organic solvent present in an exhaust gas of a printing press or the like, said system comprising an oxidation chamber, preheat means for preheating at least a portion of the exhaust gas prior to entrance of the ~xhaust gas into said chamber and combustion control means for regulating the amount of heat of combustion generated from ~he exhaust gas so as to regulate the temperature of said chamber.
In another aspect the present invention provides a method of thermal oxidation adapted to remove organic solvent from an exhaust gas of a printing press or the like, said method comprising the steps of: preheating at least a portion of the exhaus~ gas prior to introducing the exhaust gas into an , oxidation chamber; introducing the exhaust gas into the oxidation chamber; and regulating the heat of combustion generated from the exhaust gas so as to regulate the temperature in said oxidation chamber.
Advantageously, the combustion control or regulation can be carried ~; 20 out either by preheat control means for controlling the flow of said exhaust - gas through a preheater or by solvent control means for controlling the solvent ` concentration of said exhaust gas or by a combination thereof. Preferably, the preheating of at least a portion of the exhaust gas is accomplished by means ; a~apted to preheat at least a portion of the exhaust gas to the ignition tem-` perature of the solvent thereby causing the solvent to generate heat of com-bustion and adapted to use the heat of combustion to preheat said exhaust gas, for example, to at least the ignition temperature of the solvent.~ -Preferably, the combustion control or regulation includes the use of preheat control means for controlling the flow of exhaust gas through the -preheat means; the preheat control means including, for example, means for by-';', :: :

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passing a portion of the preheat means. In a particularly, preferred embodi-ment the preheat means includes a bed of heat exchanger elements or pebbles and the application of preheat is controlled by causing a portion of the ex-haust to bypass a portion of the preheater; the amount of exhaust gas bypass-ing a portion of the bed preferably being controlled in accordance with the temperature of the oxidation chamber.
Alternatively, in another preferred embodiment, the combustion controlor regulation includes the use of solvent control means to control the solvent concentration in the exhaust gas; e.g. by admixing a relatively high solvent concentration gas with a relatively low solvent concentration gas to form the exhaust gas. In particular the relatively high solvent concentration gas which is drawn from the press may be admixed with air from the pressroom ;' serving as the relatively low solvent concentration gas. Preferably, the ~' proportion of said gases is regulated-by some ~ui~a~ means.
`` In another aspect the present invention provides a method for the - conservation of energy in a thermal oxidation system adapted to remove organic solvent from an exhaust gas of a printing press or the like comprising the steps of; collecting exhaust gas containing organic solvent from the dryer `; section of a press, preheating said exhaust gas prior to introduction of same :,;, ~ ~
; ~ 20 into a thermal oxidation chamber, heating said exhaust gas within said chamber . to promote oxidation of said solvent, regulating the application of preheat .. ~
to said exhaust so as to control the heat applied to said exhaust within said oxidation chamber.
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The present invention also provides a method for the conservation of energy in a thermal oxidation system adapted to remove organic solvent from an :
exhaust gas of a printing press or the like comprising the steps of collecting `- solvent laden gas from a dryer section of a printing press, collecting solvent laden gas from the pressroom, admixing said collected gases to form an exhaust gas, preheating said exhaust gas prior to introducing same into an oxidation chamber, heating the exhaust gas in the oxidation chamber to promote oxidation, '"'~' .:

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regulating the application of heat to the oxidation chamber, and regulating the proportions of said collected gases forming said exhaust gas so as to control the application of heat to said oxidation chamber.
As indicated above, the present invention relates to a thermal oxida-tion system for removing organic solvents from the exhaust of a printing press or the like. A non-metallic preheater may be utilized to preheat the exhaust to the solvent ignition temperature causing the solvent to generate its heat of combustion. The preheated exhaust is introduced into an oxidation chamber.
, By regulating the amount of heat of combustion, the chamber temperature can be controlled to minimize fuel consumption and eliminate deterioration of the structure. Regulation of the generated heat of combustion is achieved through control of the application of preheat or of the solvent concentration of the .
exhaust. The heat from the exiting gases from the oxidation chamber is re-covered and utilized to perform the preheat operation.
In accordance with another aspect of the present invention, provides a thermal oxida~ion system which includes an oxidation chamber and a preheater in the form of first and second regeneration chambers. Each of the regenera-tion chambers has a first port and a second port, the second port of each re-generation chamber being operably connected to the oxidation chamber. Inlet and outlet means, preferably in the form of ducts or conduits, are provided and are operably connected to each of the first ports of the regeneration chambers. Means are provided for regulating the flow through each inlet means and each outlet means. A controllable heat source, such as a gas or oil fuel flame, is situated within the oxidation chamber. Means for sensing the tem-~ perature of the oxidation chamber is situated th0rein.
;~ A bed of heat exchanger elements are situated in each regeneration -: .~
chamber, between the first and second p~rts thereof. Bypass means are operably - connected to each of the regeneration chambers between the inlet means and a location within the bed therein such that gas directed along the bypass means circumvents at least a portion of the bed. Means are provided Por controlling , ', ' ' . ~ .
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the flow of gas through ~he bypass means.
Preferably, the bypass control means is operably connected to the temperature sensing means to control the flow through the bypass means in ~-accordance with the temperature in the chamber. The degree to which the in-coming exhaust as a whole is preheated is thus regulated by the amount of flow in the bypass. In this mannerJ the temperature in the oxidation chamber can be maintained at a level such that little or no fuel is required to maintain the oxidation process and generation of destructive additional heat is elimi-nated. Thus, energy conservation in the thermal oxidation system is achieved by regulating the application of preheat to the exhaust gas, and thus the generated amount of heat of combustion, in order to maintain the amount of heat in the oxidation chamber at a given level. Preheating is accomplished by heating a bed of heat exchanger elements and then passing the incoming exhaust gas therethrough. Regulation of the application of preheat is accomplished by selecting the amount of incoming gas to bypass a portion of the preheated bed.
By regulating the amount of exhaust gas which travels through the bypass, the temperature of the exhaust gas as it is introduced into the oxidation chamber, ` the amount of heat of combustion generated and thus the temperature of the chamber itself, is controlled.
The present invention in another aspect provides a thermal oxidation system adapted to remove organic solvent present in an exhaust gas of a print-ing press or the like, comprising an exhaust gas collection means, operably connected to the dryer section of said press and adapted to collect exhaust gas containing organic solvent, floor sweep ventilation means adapted to col-lect low organic solvent concentration gas from the pressroom, said floor sweep ventilation means being operably connected to said collection means, floor sweep flow regulation means interposed between said floor sweep ventila-tion means and said collection means for regulating the flow of gas from said floor sweep ventilation means, to said collection means, thermal oxidation means, and exhaust gas preheat means operably connected between said collec-`~ tion means and said oxidation means.

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More particularly, in accordance with another aspect the present in-- vention provides a thermal oxidation system including an exhaust gas collection duct which is operably connected to the dryer section of, for example, each of the print stations in a multi-stationed printing press. A floor sweep ventila-tion duct is provided in the pressroom, the floor sweep ventilation duct being operably connected to the exhaust gas collection duct. ~ control damper is interposed between the floor sweep ventilation duct and the exhaust gas collec-': ~
tion duct in order to regulate the flow from the floor sweep ventilation duct into the exhaust gas collection duct. The exhaust gas collection duct feeds 10 the preheat section of the system, which in turn is connected to the thermal oxidation chamber. Means are provided in the oxidation chamber to sense the temperature thereof. The controllable damper on the floor sweep duct is regu-lated in accordance with the temperature in the oxidation chamber.
Since the exhaust from the floor sweep ventilation duct has a solvent . . , concentration which is noramlly substantially lower than the solvent concentra-i tion from the dryer exhausts, the overall solvent concentration of the exhaust gas can be regulated by the control of the floor sweep ventilation duct damper.
In this manner, the heat of combustion generated by the solvent, as it is pre-heated above the ignition temperature, can be regulated, thereby controlling 2Q the temperature in the oxidation chamber, in order to minimize fuel consump- -tion and eliminate deterioration of the structure.
Preferably, each of the dryer sections of the printing stations is provided with a LEL tLower Explosive Limit) control device which serves to in-crease the solvent concentration level in the dryer exhaust, while substantial-ly reducing the volume thereof. This permits much more accurate control of the overall exhaust solvent concentration level by operation of the floor sweep ventilation duct damper and, in addition, permits the use of a substantially smaller oxidation chamber.
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.~ Thus, solvent laden gases are collected from the dryer sections of the printing station and from the floor of the pressroom. The collected gases are combined to form the exhaust gas. The exhaust gas is preheated prior to introduction of same into the oxidation chamber. Once in the oxidation cham-,, - 10-~ ,' , ' .
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ber, additional heat (if needed) is applied to the exhaust in order to promote oxidation. The proportions of the collected gases from the dryers and from the floor sweep duct, respectively, are regulated such that the solvent concentra-tion of the exhaust gas and thus the generated heat of combustion, is con-troll0d in order to minimize the amount of fuel required to heat the chamber and perform the floor Cweep operation without additional cost or apparatus.
During press clean up ~press not operating~ floor sweep is accomplished through the same system, the entire capacity of the oxidation chamber being utilized for this purpose.
In drawings which illustrate embodiments of the present invention:
~ Figure 1 is a side elevation view of a pressroom containing a multi-; station rotogravure in prin~ing/packaging press of the type which can be utilized in conjunction with the present invention;
Figure 2 is a side cross-sectional view of one of the printing sta-. . .
tions of the rotogravure printing press shown in Figure l;
Figure 3 is an exploded isometric view of a first preferred embodi-ment of the thermal oxidation system of the present invention.
Figure 4 is a cross-sectional view of the first preferred embodiment of the thermal oxidation system as shown in Figure 3;
- 20 Figure 5 is a cross-sectional view of a second preferred embodiment of the thermal oxidation system of ~he present invention;
Figure 6 is a schematic view of the control system for the first pre-- fe~red embodiment of the thermal oxidation system of the present invention; and ; Figure 7 is a schematic view of the control system for the second preferred embodiment of the thermal oxidation system of the present invention.
The present invention can be used with a printing press of the type shown schematically in Figure 1. Figure 1 shows a pressroom, generally de-signated A, within which is situated a multicolor, multi-station rotogravure printing/packaging press, generally designated B. Connected to the press is an exhaust gas system, generally designated C, comprising a blower, generally designated D, a thermal oxidation system, generally designated E, and the appropriate duct work connecting the blower D

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~(~920~L4 and the oxidation system E with each other, with the press and with an outlet i.~ to the environment, such as a chimney.
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Rotogravure printing/packaging press B, situated within pressroom A, is provided with a web feed and web tension control section 10, eight printing sections 12a through 12h and a cutting, creasing and/or stacking station 14.
Above each of the printing sections 12a through 12h is provided a drying sec-tion 16a through 16h, respectively. Each of the printing sections 12a through j 12h is provided with an individual control panel 18 upon which are situated ; the means for controlling the printing processes taking place in each section.
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Above the drying sections 16a through 16h is an exhaust duct 20 which :~ is individually connected to the exhaust portion of each of the dryer sections ~-i:
16a through 16h. Exhaust duct 20 is additionally connected to a floor sweep duct 22 which has a plurality of input registers 24 situated near the floor on the pressroom in order to eliminate solvents which inevitably escape from the dryer sections. Preferably, a register 24 is provided for each printing sec-tion, each register being connected to duct 22. Along floor sweep ventilation - duct 22 is provided a damper 26, controlled by a floor sweep damper control 28, which regulates the amount of exhaust gas which passes through the floor sweep ventilation duct 22 and into exhaust duct 20.
; 20 Exhaust duct 20 is connected to the input side of blower D, the outpu~ side of which is connected to the oxidation system E by means of a duct 30. The output side of oxidation system E is connected by means of a duct 31 :, to the environment through a chimney or the like (not shown).
; It is noted that the particular configuration of the rotogravure ..
press depicted in Figure 1 forms no part of the present invention. The press `~ has been shown schematically for purposes of illustration only and numerous . different types of presses having a variety of different configurations and 'i:. ...
numbers of stages are well known to the art and can be used in conjunction with the thermal oxidation system of the present invention.
Eigure 2 is a pictorial representation of the inside of any of the '~
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printing stations 12 and the dryer section 16 associated therewith. The film, paper or paperboard web 32 enters the input side of the printing station 12 passes around idler rollers 42, passes between a pair of rotatable cylinders 34, 36 and then passes into the dryer section 16. Cylinder 34 is partially immersed in an ink bath 38 and is provided with a plurality of indentations or recesses 40 distributed along the surface thereof in the appropriate locations.

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Identations 40 pick up ink from ink bath 38 and transfer same to the surface of web 32, as the web passes between cylinders 34 and 36.
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The ink utilized contains a variety of organic solven~s which are i 10 evaporated in the dryer section 16. The web in the dryer section 16 is sup-ported by a number of idler rollers 44 as it is passed in front of duct 46.
Duct 46 has a plurality of openings adj~cent the web along the path of travel .

thereof. Normally, an idler roller 44 is provided adjacen~ to each opening in order to support the web against the pressure o the incoming air from duct 46. Duct 46 is fed, by means of a blower 48 and a heater 50, with hot air in order to facilitate the evaporation of the organic ink solvents. The air from duct 46, after it is passed over ~eb 32, is returned to blower 48 by means of .:
duct 52, also situated within drying section 16, having a number of openings ~herealong to receive the incoming air. Up to this point what has been de-scribed is a completely enclosed recirculating and heating system for the dryer section.

I~ is, however, necessary to remove a portion of the recirculating air such that the concentration of the organic solvents therein does not reach , ::
a level where a spark or the like could cause an explosion. In the industry, organic solvent concentration is often measured in terms of LEL ~Lower Explo-sive Limit) and normally the organic solvent concentration within the dryer section is regulated so that it never exceeds 25% of the LEL. One way to , achieve this regulation is to continuously replace the recirculating air by exhausting same through an outlet duct 54, which is connected to exhaust duct 20. As the solvent laden air passes through outlet duct 54 fresh air is :: `

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sucked through inlet duct 56 from the pressroom. Inlet duct 56 is normally situated at the end of duct 5~. This method of replacing the recirculating air within the dryer section in an unregulated manner is effective, but will -require a rel~tively large thermal oxidation system to handie the large volume of exhaust having a relatively low solvent concentration.
In order to more efficiently regulate the solvent concentration in the recirculatlng air within dryer section 16 and thereby substantially cut down the volume of exhaust air, an LEL control is utilized within each of the dr~er sections. LEL controls of a variety of different configurations are well known in the art.
The LEL control system comprises a solvent concentration sensor 58 which is situated to sense the solvent concentration in the recirculating air. Sensor 58 generates a signal which is proportional to the organic solvent concentration level. The signal from sensor 58 is transferred to the LEL control circuit 60 which pneumatically regulates the opening and closing -of a damper 62 situated within outlet duct 5~. In this manner, the solvent cOncentration of the air within the dryer section is accurately monitored and maintained at the desired level. The use of an LEL control considerably re-duces the volume of air which passes through outlet duct 5~ and thus the volume .. . .
of air which must be therma]ly oxidized by the thermal oxidation system. Fur-ther, the LEL control acts to ensure that the solvent concentration within , the dryer will never be high enaugh to cause an explosion and may be set up i,~ to automatically stop the press if the solvent concentration reaches a : , , dangerous level due to malfunction. Thus, the LEL control serves both as a .: i safety monitoring system and as a means of reducing the volume of exhaust gas which must be processed.
r Figure 3 shows the first preferred embodiment of tlle thermal oxida-tion system of the present invention. The system itself comprises a steel j ,' .

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structure divided into two regeneration chambers 64 and 66 and a thermal oxi-dation chamber 69. The chambers are lined with precast panels of conventional furnace material, approximately six inches thick, such as are commercially available from the Quigley Company Inc. of New York, New York. The composition ; and thickness of the precast panels is determined, at least in part, by the operating temperatures of the chambers. In this example the chambers are de-signed to withstand a temperature of up to approximately 2000F but will nor-mally be operated below this temperature. It is necessary, in order to pre-vent costly maintenance and a substantial shortening of useful life of the structure~ to monitor and regulate the temperature in the system.
Each of the regeneration chambers 64 and 66 has a first port 68, 70, respectively and a second port 72, 74, respectively. Second ports 72 and 74 of regeneration chambers 64, 66 open into oxidation chamber 69. The first . .
- ports 68, 70 of the regeneration chambers are connected to an input-output . .
manifold 76, which in turn is connected to duct 30 from blower D and duct 31 leading to the chimney. Manifold 76 is divided into two sections, 76a, 76b ~ which are operably connected to first ports 68, 70 respectively. Section 76a ~ is connec~ed to duct 30 through a damper 78a. Likewise, section 76b is con-nected to duct 30 through a damper 78b. In order to connect the system to the environment, section 76a is connected to duct 31 by means of a damper 80a and section 76b is connected to duct 31 by means of a damper 80b.
Each of the regeneration chambers 64, 66 is a four sided structure, , ~
;-~ with the first and second ports forming the remaining two opposite sides.
s Situated within each of the regeneration chambers 64, 66 is a bypass duct 82, :
: 84 which has a length which is somewhat shorter than the length of the re-:.
generation chamber in which it is situated. In other words, the bypass ducts 82, 84 do not extend the entire length of the regeneration chambers. The entire regeneration chamber, aside from the bypass duct itself, is filled with a heat exchanger substance preferably in the form of "pebbles" in order to form a pebble bed heat generator, of the type developed around 1929 by the .. ~.

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~ United States Department of Agriculture to replace the heat exchanging struc-i; .
ture for the classical brick checkerwork construction, commonly employed at ~hat ~ime as an air preheater for blast furnaces. Preferably, the "pebbles"
are of the type sold by the Norton Company, of Akron, Ohio, under the trade-mark INTALOX, which have a saddle shape. Such a shape has been found to be effective to provide the maximum usable area for heat exchange with a minimum resistance to the gas flow through the column. The non-symmetrical nature of the saddle shape permits the elements to be packed randomly, while assuring maximum surface and minimum gas flow resistance. This type of bed serves to throughly mix the solvent laden air such that the air, as it enters the oxi-dation chamber, is uniform enough to permit oxidation as the exhaust exits the bed thereby reducing the size of the oxidation chamber by beginning the re-quired dwell time of approximately .6 seconds immediately. It is noted that a screen or other barrier ~not shown) is provided at the exit side of bypass ducts 82, 84 and at the second port of regeneration chambers 64, 66 such that : the elements of the pebble bed are retained in the appropriate locations.
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; The oxidation system operates as follows, neglecting for the moment ,; the functioning of the bypass ducts 82, 84. Solvent laden air from the dryer :~ sections 16 is collected in exhaust duct 20 and moved by means of blower D, through duct 30. Inlet damper 78a is opened and inlet damper 78b is closed such that the solvent laden exhaust gas enters only section 76a of manifold 76. The solvent laden exhaust gas passes through first port 68 of regeneration ~; chamber 64 and then through the pebble bed 86 contained therein. Pebble bed ,,~
86 has been preheated by passing the exhaust gas exiting the oxidation chamber - 69 therethrough, during a previous cycle. The solvent laden exhaust gas pas-~ sing through pebble bed 86 is preheated by the bed, which is designed to effi-"~ .
~- ciently transfer the heat stored therein to the solvent laden exhaust gas.

The solvent laden exhaust gas passes along the entire length of regeneration chamber 64, and thus through the pebble bed 86 situated therein, until it ~`~ 30 reaches second port 72, through which it passes. The preheated exhaust gas .
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2~3L4 .:i is then in~roduced into oxidation chamber 69.
~- Oxidation chamber 69 is provided with a burner 90 and a temperature sensor 92. The burner is connected to a source of natural gas, oil or some other appropriate fuel (not shown) and the size of the flame, and therefore the amount of heat applied to the solvent laden exhaust gas in the oxidation cham-; ber 69l can be regulated. It is necessary, in order to transform 99% of the organic solvents into harmless carbon dioxide and water vapor, to heat the solvent laden exhaust gas to at least 1400F, for about .6 seconds. Thus, the oxidation chamber must be designed such that the solvent laden exhaust gas passing therethrough will be at the oxidation temperature for at least the necessary time. In order to prevent any of the solvent laden exhaust gas from "short circuiting" a portion of the oxidation chamber and thus passing from one regeneration chamber to the other in less than the required *ime, a baffle structure 94 is provided within the chamber. However, since the entire cham-~' ber is maintained 1400F level or above, it is not necessary in this system for the exhaust gas to pass directly through the flame, as common with exist-ing thermal oxidation units that require the use of gas as a fuel.
` The oxidized exhaust gas exits the oxida~ion chamber 69 through : second port 74 of regeneration chamber 66. The oxidized exhaust gas then travels along the length of regeneration chamber 66, thus through the pebble . . .
bed 88 situated therein, through first port 70 and into section 76b of mani-:
fold 76. Damper 80b in section 76 is opened such that the oxidized exhaust ; gas travels through duct 31 and subsequentIy to the environment. As the oxi-dized exhaust gas passes through pebble bed 88, much of the heat therein is transferred to the pebble bed. This heat will be used to preheat the incoming solvent laden exhaust gas during the next cycle.
After a given timel for example 10 minutes, when pebble bed 86 no longer has sufficient heat to preheat the solvent laden incoming exhaust gas, and pebble bed 88 has absorbed as much heat as possible from the outgoing ; 30 oxidized exhaust gas~ the gas flow path is reversed. This is accomplished by . ~
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, closing damper 78a and opening damper 78b such that incoming gas from duct 30 goes into section 76b of manifold 76. In addition, damper 80b is closed and damper 80a opened such that oxidized exhaust gas from regeneration chamber 64 can enter duct 31 and thus be trans~erred to the environment. In this mode, ~,~, the solvent laden exhaust gas passes through first port 70 of regeneration cham-. ., ber 66, through pebble bed 88, which preheats same, and then through second , port 74 into oxidation chamber 69. The oxidized exhaust gas from oxidation chamber 69 enters regeneration chamber 64 through second port 72, wherein the ' heat thereof is utilized to reheat pebble bed 863 the oxidized exhaust gas :`~: 10 passes along the length of regeneration chamber 64 to first port 68 thereof and finally through section 76a of manifold 76 and damper 80a into duct 31.
~` It should be appreciated that the oxidation system of the present invention may include more than two pebble beds. However, for simplicity of ~, explanation, only two pebble beds have been described herein for purposes of illustration.
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: 1 From this brief description it can be seen that by merely closing and opening the appropriate dampers, the gas flow through the oxidation system can r,'~l be alternately directed first through one regeneration chamber and then the other, in order to recover the heat of the oxidized outgoing exhaust gas and ~, .-; 2Q utilize same to preheat the incoming solvent laden exhaust gas. Such a~system, when operated at trace LEL, results in energy savings of approximately 85% over i` the use of an oxidation chamber without hea~ recovery. Thus, at trace LEL, only approximately 15% of the fuel which would normally be required is neces-;.` sary to perform the oxidation process ~hrough the use of the pebble heat gener-ator. As the solvent level increases above trace LEL, as described below, the heat of combustion of the solvents can be utilized to further reduce the fuel requirements to nearly zero.
In conjunction with the abo~e description, it must be appreciated ,! ~
that organic solvents of the type considered herein will generate considerable ` 30 amounts of heat combustion, when same are preheated above their ignition tem-- peratures. The amount of heat of combustion generated by the solvent laden '' :
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exhaust gas will depend upon the temperature to which the organic solvents are preheated and the concentration of organic solvents present. It should also be recalled that the oxidation chamber has a certain permissible operation temperature which, if exceeded, will cause deterioration thereof requiring costly maintenance and reducing the useful life of the chamber. It is the essence of applicant's invention to control the amount of heat of combustion generated by the solvent laden air, in order to minimi~e the fuel consumption of the oxidation chamber as well as to maintain the temperature therein below the level where the structure will deteriorate. This result may be achieved i 10 by two separate preferred methods, represented herein by the first preferred embodiment and second preferred embodiment, respectively.
In the first preferred embodiment, the hea~ of combustion generated by the solvent laden exhaust gas is controlled by controlling the amount of preheat applied. This is accomplished through the use of bypass ducts 82 and 84 and dampers 96 and 98 associated therewith. Damper 96 controls the amount of solvent laden exhaust gas which passes from section 76a of manifold 76 through bypass duct 82. Likewise, damper 98 controls the amount of solvent laden exhaust gas which passes from section 76b of manifold 76 through bypass duct 84.
The manner in which the bypass system operates is at best illustrated with reference to Figure 4, which shows a cross-sectional view of the system taken through regeneration chamber 64. As can be seen in this drawing, when damper 96 is opened, solvent laden exhaust gas is permitted to pass from sec-tion 76a through bypass duct 82. The gas in duct 82 passes through only a small portion of the pebble bed 86, bypassing the portions thereof surrounding the bypass duct. In this manner, the gas which passes through the bypass duct 82 is preheated to a much lesser extent than the gas which passes thrGugh the remainder of regeneration chamber 64. Therefore, the amount of preheat applied to the solvent laden exhaust gas, as a whole, passing through the re-,,:.

generation chamber is regulated by the opening and closing of the bypass , ~

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; damper. As a result, the heat of combustion generated by the solvents in the , solvent laden exhaust gas is controlled such that virtually no additional heat need be imparted to the solvent laden exhaust gas within the oxidation chamber 69 ~o sustain the oxidation process and in addition the temperature within , the oxidation chamber 69 can be maintained below destructive levels. In this manner, fuel consumption is reduced to almost zero ~it is more convenient to keep the burner flame at the pilot level instead of shutting it off completely) and the maintenance and replacement costs for the oxidation chamber are virtu-ally eliminated. Bypass dampers 96 and 98 are connected to operate together such that the efficiency of both the preheat bed and the exhaust bed is re-~; duced simultaneously.
',;j The systemJ as it has been considered up till now, has been run with ~ the floor sweep duct damper closed so that only exhaust gas from the dryer . ~
sections of the printing stations has been processed. ~hen permitted, the floor sweep ventilation system can be vented directly to the atmosphere while ;, .
, the press is running. This may be accomplished by an additional duct section and blower (not shown in the drawings) directly connecting duct 22 to duct 31 and a damper ~also not shown) which controls the flow therethrough. This damper will be opened only when the press is running. Since the solvent level `; , .
concentration of the pressroom air is relatively small during the running of the press, this mode of operation will not adversely affect the environment.
In the first preferred embodiment of the system, processing of the air from the floor sweep ventilation system will occur only during press clean up (after the press has ceased to operate), at which time the solvent level con-centration thereof is somewhat higher. However, during press clean up, the bypass dampers will remain closed because the solvent concentration of the air from the floor sweep ventilation system will normally still be below the level wherein the amount of heat of combustion generated is sufficient to sustain the oxidation process.
.
, 30 As illustrated in Figure 5, which shows the second preferred embodi-,'.................................................................... .
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It should be appreciated that as the solvent concentration oE the dryer exhaust increases, damper 26 will open more, thereby increasing the volume oE gas passing through the floor sweep ventilation system. Thus, the efficiency of the floor sweep ventilation system is increased during periods of greatest necessity, such that the atmosphere in the pressroom is always maintained at acceptable solvent concentration levels. Further, during press-room clean up (after the operation of the press has ceased~ when all of the exhaust processed by the oxidation system comes from the floor sweep ventila-tion system (as described below), the oxidation system of the present inven-tion will consume only 15% of the amount of fuel required by a system without heat racovery, even though the solvent level concentration is rela~ively low.
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is efficiently utilized ~o eliminate solvents in the pressroom air.
By regulating the amount of gas introduced from the floor sweep ventilation system, it is possible to accurately regulate the solvent concen-tration of the preheated exhaust gas as same enters the oxidation chamber and thus the amount of heat of combustion generated thereby. By controlling the generated heat of combustion it is possible to run the oxidation system with virtually no fuel and prevent deterioration of the structure and at the same time provide an efficient floor sweep ventilation system without any additional cost or equipment.
As mentioned above, it is common in the industry to include a LEL
monitor and control within each of the dryer sections. Such a control permits the accurate regulation of the solvent concentration of the gas exiting the dryer sections while substantially reducing the volume of the exhaust. If the system of the second preferred embodiment of the present invention is utilized in conjunction with LEL controls in each dryer section, it will be possible to more accurately control the solvent concentration of the combined floor sweep ventilation system and dryer ventilation system in order to maintain the amount of heat of combustion generated within the oxidation chamber to -the most efficient level.
,` 20 Thus, the second preferred embodiment controls the amount of heat of combustion gener~ted by the solvents within the oxidation chamber, as does the first preferred embodiment, but has the additional advantage of providing a floor sweep ventilation system at no additional cost. Further, like the first preferred embodiment, the second preferred embodiment may be utilized during clean up, when the press has ceased to function, solely as a pressroom floor sweep ventilation system, without duplication of equipment.
It should also be noted that further energy conservation can be achieved by utilizing the unrecovered heat present in the output of the oxida-tion system. A certain amount of heat remains uncollected by the pebble bed and the temperature of the exhaust gas from the oxidation system may be in ~ .

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excess of 300F. This hot oxidized exhaust gas can be used to heat oil or other fluid which can then be circulated through the dryer sections to heat the air therein.
Figure 6 is a schematic diagram of the bypass damper control system of the first preferred embodiment of the present invention. As shown in Fig-ure 6, the output of temperature sensor 92, of conventional design5 is con-nected to a burner control 100. Sensor 92 generates an electric signal which is a function of the temperature in the chamber. A burner control 100, of conventional design, is provided to regulate the amount of fuel which is introduced into burner 90, and therefore the amount of additional heat which is applied to the solvent laden gases within the oxidation chamber. The re-gulation of the fuel by burner control 100 can be performed in any conventional manner, such as through the use of a solenoid operated valve or the like.
Preferably, burner control 100 is designèd to provide a minimum amount of fuel : : .
to burner 90 such that, even when the temperature in the oxidation chamber is above the necessary level, the burner flame is at the pilot level. This elimi-nates the necessity for subsequently relighting the flame. Through the use of the control loop described, only the amount of heat will be applied to oxida-tion chamber 69 by burner 90 which is required to sustain the oxidation pro-: .~ .
cess.
- As indicated above, the heat of combustion generated by the incoming ~ solvent laden exhaust gas, as same is preheated above the ignition temperature ; thereof, is of*en more than enough to maintain the oxidation chamber at therequired 1400F to sustain the oxidation process. Once the amount of heat of . combustion which is generated causes the oxidation chamber temperature to rise above a present level, the bypass system of applicant's first preferred embodi-ment is utilized to prevent the generation of any additional excess heat.
Thus, temperature sensor 92 is also connected to bypass damper control 102.
; Damper control 102 is a conventional, commercially available system which con-verts the signal output of sensor 92 into a pneumatic or hydraulic pressure or ;
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an electric signal. Thus, when bypass damper control 102 senses an input signal above a given magnitude, the bypass dampers ~dampers 96 and 98 are con-nected to operate together) of the oxidation system will be opened. Since the output of control 102 is a function of the temperature sensed, the dampers will open to a greater degree the higher the temperature. Bypass damper con-trol 102 is pneumatically, hydraulically or electrically connected to the by-pass dampers, in a manner which is well known in the art, such that the posi-tion of th0 dampers can be accurately controlled in accordance with the sensed temperature. Dampers 96 and 98 may be pneumatically (or hydraulically) operat-ed or may be driven by an electric motor. However, pneumatically or hydrauli-cally dampers are preferred because of the explosive environment. Thus, by-pass damper control 102 is preferably an electric to pneumatic (or hydraulic) transducer which regulates the pneumatic (or hydraulic) pressure in accordance with an electric input signal generated by temperature sensor 92. However, entiraly electrical systems can be used if same are suitably protected against the explosive environment.
Figure 7 is a schematic diagram of the control system for the second preferred embodiment. In this system, the temperature sensor 92, burner con-trol lO0 and burner 90 operate essentially as described above. However, in this embodimentl the signal from temperature sensor 92 is transmitted to floor sweep damper control 28 which, like bypass damper control 102, is an electrical .
to pneumatic or hydraulic (or electric) transducer which causes the floor sweep damper 26 to open or close in accordance with the signal from temperature sen-sor 92. In this case, when the temperature sensed within the oxidation cham-i.
ber reaches a level above a preset temperature, burner control 100 sets burner ~; 90 at the pilot condition. As the temperature exceeds this levelJ the floor sweep damper control 28 will cause damper 26 to open, thereby permitting air . .
` from the floor sweep ventilation system into ~he duct 30 and thus reducing the -~ solvent concentra~ion of ~he solvent laden gases in the oxidation system.
It should also be noted that floor sweep damper control 28 has a : *
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second input, which is connected to the output of floor sweep initiation con-trol 104, which is located at a convenient position, such as the press master control panel. Floor sweep initiation control 104 serves to generate a signal actuating floor sweep damper control 28 to open damper 26 all the way when the press has ceased to function and the oxidation system is to be used exclusively for floor sweep purposes. In this latter mode, the signal from temperature sensor 92 will have no effect on the position of damper 26 but will continue to regulate burner control 100 so as to assure that the oxidation chamber re-mains at ~he necessary temperature to perform the oxidation process. ~hen the 10 system is in the floor sweep mode, additional heat will normally be applied to the oxidation chamber through burner 90 because the solvent concentration of the exhaust from the floor sweep ventilation system will normally not be suffi-ciently high to generate enough heat of combustion to sustain the system with-out fuel consumption.
It should now be appreciated that the present invention relates to .... .
control of the amount of heat of combustion which is generated by solvent laden gases and especially solvent laden gas preheated in an oxidation system to a level above their ignition temperature. One preferred method relates to the regulation of the degree of preheat which is applied to the solvent laden gases, as a whole, Another preferred method relates to the use of the floor sweep ventilation system to reduce the solven~ concentration of the exhaust in a controlled manner thereby also regulating the amount of heat of combustion generated.
~` Thus, the present invention provides a method and apparatus for use on a thermal oxidation system for use on a multi-station rotogravure packag-ing/prin~ing press, which can not only minimize the amount of fuel required by the oxidation system but also reduce the maintenance costs and enhance the useful life of the oxidation structure. These results are accomplished by monitoring of the temperature within the oxidation chamber and the control of ` 30 the amount of heat of combustion generated in accordance therewith.
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In addition, the second preferred embodiment described above in-cludes a floor sweep ventilation system which operates continuously as the press is operated. As more solvent is used in each printing unit, a higher solvent concentration will be present in the dryer exhaust and more solvent will be evaporated into the pressroom air. The increased solvent concentra-tion in the dryer exhaust will cause an increase in the floor sweep volume, thereby automatically increasing the efficiency of the floor sweep system in order to clean pressroom air more efficiently.
While only two preferred embodiments of the present invention have been described herein for purposes of illustration, it is obvious that many modifications and variations could be made thereto. It is intended to cover all of these variations and modifications that fall within the scope of ,,.:; :
applicant's invention as defined by the following claims.
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Claims (47)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A thermal oxidation system adapted to remove organic solvent present in an exhaust gas of a printing press or the like, said system comprising an oxidation chamber, preheat means for preheating at least a portion of the exhaust gas prior to entrance of the exhaust gas into said chamber and combus-tion control means for regulating the amount of heat of combustion generated from the exhaust gas so as to regulate the temperature of said chamber.

2. A thermal oxidation system as defined in claim 1 wherein the com-bustion control means includes either preheat control means for controlling the flow of said exhaust gas through said preheat means or solvent control means for controlling the solvent concentration of said exhaust gas or a combination of said preheat control means and said solvent control means.

3. A thermal oxidation system as defined in claim 2 wherein the com-bustion control means includes said preheat control means.

4. A thermal oxidation system as defined in claim 3 wherein said pre-heat control means includes means for bypassing a portion of said preheat means.

5. A thermal oxidation system as defined in claim 1 wherein said pre-heat means includes means for preheating said exhaust gas by preheating at least a portion of the exhaust gas to the ignition temperature of the sol-vent thereby causing the solvent in said portion to generate heat of com-bustion.

6. A thermal oxidation system as defined in claim 5 wherein said pre-heat means includes means for preheating the preheated exhaust gas to at least the ignition temperature of said solvent.

7. A thermal oxidation system as defined in claim 5 wherein said com-bustion control means includes preheat control means for controlling the flow of exhaust gas through said preheat means.

8. A thermal oxidation system as defined in claim 7 wherein said pre-heat control means includes means for bypassing a portion of said preheat means.

9. A thermal oxidation system as defined in claim 8 wherein said pre-heat means includes a bed of heat exchanger elements and wherein said preheat control means includes means for causing a portion of said exhaust to bypass a portion of said bed.

10. A thermal oxidation system as defined in claim 9 wherein said pre-heat control means includes bypass portion control means to control the amount of said exhaust gas bypassing said portion of said bed.

11. A thermal oxidation system as defined in claim 10 including means for sensing the temperature of said oxidation chamber and means operably connecting said sensing means and said portion control means such that the amount of said exhaust gas bypassing said portion of said bed is controlled in accordance with said sensed temperature.

12. A thermal oxidation system as defined in claim 5 wherein said combustion control means includes solvent control means for controlling the solvent concentration of the exhaust gas.

13. A thermal oxidation system as defined in claim 12 wherein said solvent control means includes means for admixing a relatively high solvent concentration gas from a printing press with a relatively low solvent concen-tration gas to form the exhaust gas.

14. A thermal oxidation system as defined in claim 13 including means for regulating the proportion of said high solvent concentration gas to said low solvent concentration gas.

15. A thermal oxidation system as defined in claim 14 including a print-ing press floor sweep ventilation means wherein said relatively low solvent concentration gas is collected by said floor sweep ventilation means.

16. A method of thermal oxidation adapted to remove organic solvent from an exhaust gas of a printing press or the like, said method comprising the steps of: preheating at least a portion of the exhaust gas prior to introducing the exhaust gas into an oxidation chamber; introducing the exhaust gas into the oxidation chamber; and regulating the heat of combustion generat-ed from the exhaust gas so as to regulate the temperature in said oxidation chamber.

17. A method as defined in claim 16 including the step of preheating at least a portion of the exhaust gas to the ignition temperature of the solvent to cause the solvent in said portion to generate heat of combustion and using said heat of combustion to preheat said exhaust gas.

18. The method as defined in claim 17 wherein the step of regulating the generation of heat of combustion includes the step of controlling the application of preheat applied to the exhaust gas.

19. The method as defined in claim 18 wherein the step of controlling the application of preheat includes the step of causing a portion of the exhaust gas to bypass a portion of the preheater.

20. The method as defined in claim 19 wherein the step of preheating includes heating pebbles of a pebble bed heat generator and passing exhaust gas through said bed heat generator and wherein the step of controlling the application of preheat includes the step of causing a portion of the exhaust gas to bypass a portion of said bed.

21. The method as defined in claim 20 including the step of controlling the amount of exhaust gas which bypasses a portion of the bed.

22. The method as defined in claim 17 wherein the step of regulating the heat of combustion generated includes the step of controlling the solvent concentration in the exhaust gas.

23. The method as defined in claim 22 wherein the step of controlling the solvent concentration includes the step of mixing a relatively high sol-vent concentration gas with a relatively low solvent concentration gas to form the exhaust gas.

24. The method as defined in claim 23 including the step of regulating the proportion of said high solvent concentration gas to said low solvent concentration gas.

25. The method as defined in claim 24 including the step of collecting air from a pressroom and utilizing same as a low solvent concentration gas.

26. A thermal oxidation system adapted to remove organic solvent present in an exhaust gas of a printing press or the like, comprising an oxidation chamber, first and second regeneration chambers, each of said regeneration chambers having a first port and a second port, said second port of each re-generation chamber being operably connected to said oxidation chamber, inlet and outlet means, a pair of inlet and outlet means being operably connected to each of said first ports, means for regulating the flow through each of said inlet means and each of said outlet means, a controllable heat source in said oxidation chamber, a bed of heat exchanger elements situated in each of said regeneration chambers between said first and second ports thereof, bypass means operably associated with each of said regeneration chambers and connected between said inlet means and a location in said bed therein, said bypass being adapted to provide a path whereby at least some exhaust gas from said inlet means may bypass at least a portion of said bed, and means for controlling the flow through said bypass means.

27. The system as defined in claim 26 including means for sensing the temperature in said oxidation chamber and means for operably connecting said bypass control means to said sensing means to control the flow of exhaust gas through said bypass means in accordance with said sensed temperature.

28. The system as defined in claim 27 including means for controlling said heat source, said heat source control means being operably connected to said temperature sensing means and capable of controlling said heat source in accordance with said sensed temperature.

29. The system as defined in claim 28 wherein said bypass means comprises a conduit situated within said regeneration chamber having an exit port situ-ated in said bed.

30. The system as defined in claim 29 wherein said conduit has a length less than the length of said regeneration chamber.

31. A thermal oxidation system adapted to remove organic solvent present in an exhaust gas of a printing press or the like, comprising an exhaust gas collection means, operably connected to the dryer section of said press and adapted to collect exhaust gas containing organic solvent, floor sweep ven-tilation means adapted to collect low organic solvent concentration gas from the pressroom, said floor sweep ventilation means being operably connected to said collection means, floor sweep flow regulation means interposed between said floor sweep ventilation means and said collection means for regulating the flow of gas from said floor sweep ventilation means, to said collection means, thermal oxidation means, and exhaust gas preheat means operably con-nected between said collection means and said oxidation means.

32. The system as defined in claim 31 including means for sensing the temperature in said oxidation means and means operably connecting said sensing means and said floor sweep floor regulation means for regulating the flow of gas from said floor sweep ventilation means in accordance with said sensed temperature.

33. The system as defined in claim 32 including means for sensing the solvent concentration level within the dryer section of the press, dryer section gas flow regulation means for regulating the gas flow from the dryer section to said collection means and means for controlling said dryer section gas flow regulating means in accordance with the solvent concentration level sensed within the dryer section.

34. The system as defined in claim 33 including heating means located within said oxidation means and means for regulating said heating means in accordance with said sensed temperature.

35. The system as defined in claim 34 including means for controlling both said floor sweep flow regulation means and said heating means.

36. The system as defined in claim 35 wherein the solvent concentration level in the exhaust gas is regulated by said floor sweep flow regulation means and said dryer section gas flow regulation means.

37. The system as defined in claim 33, including means for causing said dryer section gas flow regulation means to permit gas flow therethrough when said press is not operating such that the capacity of said oxidation means is utilized for pressroom clean-up.

38. A method for the conservation of energy in a thermal oxidation system adapted to remove organic solvent from an exhaust gas of a printing press or the like comprising the steps of; collecting exhaust gas containing organic solvent from the dryer section of a press, preheating said exhaust gas prior to introduction of same into a thermal oxidation chamber, heating said exhaust gas within said chamber to promote oxidation of said solvent, regulat-ing the application of preheat to said exhaust so as to control the heat applied to said exhaust within said oxidation chamber.

39. The method as defined in claim 38 wherein the step of preheating includes heating a bed of heat exchange elements and passing said exhaust through said bed wherein said bed has been previously heated by hot oxidized exhaust gas leaving the oxidation chamber.

40. The method as defined in claim 39 wherein the step of regulating the application of preheat includes the step of causing a portion of the exhaust to bypass a portion of said bed.

41. The method as defined in claim 40 wherein the step of regulating the application of preheat includes the step of regulating the flow of exhaust gas bypassing a portion of said bed.

42. The method as defined in claim 41 wherein the step of regulating the application of preheat includes the step of sensing the temperature in the oxidation chamber and regulating the flow of the exhaust gas bypassing a por-tion of said bed in accordance with the sensed temperature.

43. The method as defined in claim 38 or 39 including the step of sens-ing the temperature within the oxidation system and regulating the applica-tion of heat to the exhaust gas in accordance therewith.

44. A method for the conservation of energy in a thermal oxidation sys-tem adapted to remove organic solvent from an exhaust gas of a printing press or the like comprising the steps of collecting solvent laden gas from a dryer section of a printing press, collecting solvent laden gas from the pressroom, admixing said collected gases to form an exhaust gas, preheating said exhaust gas prior to introducing same into an oxidation chamber, heating the exhaust gas in the oxidation chamber to promote oxidation, regulating the application of heat to the oxidation chamber, and regulating the proportions of said collected gases forming said exhaust gas so as to control the appli-cation of heat to said oxidation chamber.

45. The method as defined in claim 44 wherein the step of regulating the proportion of the collected gases forming the exhaust gas includes the step of controlling the amount of gas collected from the pressroom floor.

46. The method as defined in claim 45 wherein the step of regulating the proportion of gases forming the exhaust gas includes the steps of sensing the solvent concentration level of the gas within said dryer section of the print-ing press and regulating the amount of gas collected from said dryer section in accordance with the sensed solvent concentration level.

47. The method as defined in claim 44 or 46 wherein the step of regulat-ing the application of heat includes the steps of sensing the temperature in the oxidation chamber and controlling the application of heat to said oxi-dation chamber.